Brain development involves orderly generation of distinct types of neurons, establishment of stereotyped neuronal connections, and developmentally programmed as well as activity-dependent remodeling of neuronal projections. In addition, like neurons, glial cells are integral to both formation and function of the brain. To elucidate the molecular mechanisms governing brain development, we propose to continue studying post-embryonic development of the Drosophila brain that involves various interesting developmental phenomena, such as extensive neurogenesis and gliogenesis in functional neural circuits and large-scale remodeling of neural circuits during metamorphosis. First, we will identify additional molecules required for various aspects of post-embryonic development of the Drosophila brain via isolating and characterizing more mushroom body mutants. Second, we will investigate whether and how numerous distinct DSCAM molecules operate collaboratively and/or differentially to mediate diverse cell type-specific neuronal morphogenesis. Third, we will develop novel MARCM technology for examining post-embryonic neurogenesis and gliogenesis systematically and simultaneously. Studying post-embryonic development of the Drosophila brain promises to shed new light on how complex neural circuits form in human brains. In particular, we expect to gain novel insights into the molecular mechanisms that govern (1) derivation of different types of neurons from common precursors, (2) chronologically appropriate neuronal morphogenesis, (3) formation/extension/guidance/arborization of dendrites versus axons, (4) remodeling of neuronal projections, (5) diverse cell type-specific neuronal morphogenesis, and (6) neuron-glial interactions.